Moon-10/00 Zaida

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Specifications	Moon-10/00 Zaida
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278-s| OCTOBER 2000 RESEARCH/DEVELOPMENT/RESEARCH/DEVELOPMENT/RESEARCH/DEVELOPMENT/RESEARCH/DEVELOPMENT ABSTRACT. Microstruct

Specifications	Moon-10/00 Zaida
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Content	278-s\| OCTOBER 2000 RESEARCH/DEVELOPMENT/RESEARCH/DEVELOPMENT/RESEARCH/DEVELOPMENT/RESEARCH/DEVELOPMENT ABSTRACT. Microstructural evolution re- sulting from gas metal arc welding of HSLA-100 steel plate with an experi- mental ultra-low-carbon weld consum- able, designated CTC-03, was investi- gated by transmission electron microscopy, optical microscopy and mi- crohardness analyses. A color micro- hardness map was generated from more than 1600 diamond indentation mea- surements taken across the transverse cross section of the weldment, to make a direct correlation between the micro- hardness variations and the correspond- ing microstructures. Eight characteristic areas of the CTC-03/HSLA-100 weld were selected to study the corresponding microstructure by TEM and optical mi- croscopy, and the microstructures were then correlated with the microhardness map. The microstructure throughout the fusion zone (FZ) consists of a majority of lath ferrite with varying amounts (de- pending on the location) of untempered fine-lath martensite, some interlath re- tained austenite, and spherical oxide in- clusions. The softest regions of the fusion zone are in curved white bands located at the lower portions of the heat-affected zones of the weld beads. The mi- crostructure within these white bands is predominantly lath ferrite. The hardest regions in the fusion zone are located be- tween the bead boundaries and these white bands, and contain significant amounts of fine untempered lath marten- site. The base plate heat-affected zone (HAZ) consists of a mixture of untem- pered lath martensite and coarse au- totempered plate martensite. The as- received HSLA-100 base metal exhibits a quench-and-tempered microstructure with a majority of fine-lath martensite and significant amounts of coarse martensite. Despite its low heat input, the CTC-03 weldment exhibits hardness val- ues comparable with those of the HSLA- 100 base metal and similar to some weld- ments made with other filler metals. The microhardness map of this weld was compared to four other microhardness maps developed for welds made with other candidate ULC filler metals and/or different heat inputs. In all five weld- ments studied, the midsection of the HAZ of the base metal (i.e.,the region located about midway between the weld inter- face and the outer boundary of the HAZ) is the hardest region of the weld, regard- less of base metal, filler metal type or heat input. Introduction The family of high yield (HY) strength steels, including HY-80, HY-100 and HY- 130, has been extensively used by the U.S. Navy since its development in 1946 (Ref. 1). The strength and toughness of these steels are derived from the forma- tion of quenched and tempered marten- site. While carbon plays a major role in the strengthening mechanism of these steels through the formation of fine dis- persions of carbides, it can also promote the formation of deleterious untempered martensite microstructures during fast cooling. These deleterious microstruc- tures have an enhanced susceptibility to hydrogen-assisted cracking (Ref. 2). Thus, welding of these steels requires strict control of the heat input and pre- heat/interpass temperature to ensure the production of acceptable microstruc- tures and mechanical properties. Since these constraints on the welding opera- tional envelope are very costly, the U.S. Navy has pursued, since about 1980, high-strength low-alloy (HSLA) steels as a replacement for HY steels. HSLA steels are lower carbon, cop- per-precipitation-strengthened steels that meet the strength and toughness require- ments of HY steels, yet are more easily welded without preheat. Use of these HSLA steels in surface ship and subma- rine construction can result in significant reductions in production costs through the minimization or elimination of pre- heat, utilization of a wider range of en- ergy inputs and employment of more re- laxed fabrication control (Refs. 3–7). However, welding consumables that take full advantage of the benefits of HSLA base metal have yet to be developed, cer- tified and put into production (Refs. 1, 5). Welding consumables originally de- signed for HY-steels are currently being used to weld HSLA steels for limited ap- Microhardness Variations in HSLA-100 Welds Fabricated with New Ultra-Low-Carbon Weld Consumables BY D. W. MOON, R. W. FONDA AND G. SPANOS HSLA-100 steel weldments made with ultra-low-carbon consumables were investigated by TEM and microhardness mapping analyses KEY WORDS HSLA-100 Microhardness Ultra-Low Carbon High-Strength Steel Naval Ships Filler Metal Hydrogen CrackingD. W. MOON, R. W. FONDA and G. SPANOS are with the Naval Research Laboratory, Washington, D.C.
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Following Datasheets	10-2000-NELSON-s (11 pages) 10-2002-HUANG-s (12 pages) 10-2002-VIANCO-s (10 pages) 10-2002-XIE-s (8 pages) 10-2003-COLLINS-s (8 pages) 10-2003-GOULD-s (5 pages) 10-2003-MENDEZ-s (11 pages) 10-2003-SOLOMON-s-1 (10 pages) 10-2003-VIANCO-s (10 pages) 10-2004-KIMAPONG-s (6 pages)
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